Vehicle manufacturers are implementing lighter, stronger materials, such as aluminum alloys to meet emission reduction goals, meet fuel economy goals, reduce manufacturing costs, and reduce vehicle weight. Increasingly demanding safety standards must be met while reducing vehicle weight. One approach to meeting these competing interests and objectives is to use aluminum extrusions with complex profiles.
Extrusion lineals having complex, non-round cross-sections are typically extruded from an aluminum billet through a porthole extrusion die at a high temperature and at high pressure. Discontinuous material flow across the section of the shape occurs when the flowing aluminum separates in the mandrel plate and re-converges in the cap section of the porthole extrusion die. The extruded structural tubes are cooled after extruding. Extruded structural tubes tend to twist, lack straightness and may be otherwise deformed during cooling and may be out of conformance with part specifications. The lineals may be extruded in lengths exceeding 100 ft. Those lengths are then stretched up to 5 percent to straighten and reduce twist to within industrially accepted Aluminum Association dimensional limits. Stretching in accordance with Aluminum Association limits does not sufficiently correct the tolerances for automotive use. The lineals are cut to a reduced length as required for the final product, a specified manufacturing blank, or for shipping
The cross-section of extruded tubes is constant along the length of the lineal. A significant advantage of extrusion technology is the flexibility to tailor the cross-section design to include multi-hollow sections having external flanges, internal ribs defining multiple cavities, and varied thickness across the section. Such flexibility supports the design of weight efficient cross-sections with high section stiffness. These tubes are typically used in front and rear bumpers, crash boxes, sports car front headers, and a-pillars.
Such parts usually have a sweeping single-axis or multi-axis bend along the length of the part which may be achieved by stretch-bending the extruded lineal tube. Stretch bending can be done with stretch-bend tooling in a press or a hydraulic, purpose-built stretch-bending machine. In stretch-bending, the straight extruded tube blank is gripped at the ends of the tube. The tooling then moves to simultaneously stretch and bend the tube onto a one-sided, matched tooling. This process serves to both shape (sweep) the part along the length as well as improve the tolerance of the component to a level acceptable for automotive applications. This type of bending action cannot be utilized for an extrusion part that is designed to be straight in an automotive application. Although stretching and bending together can improve dimensional tolerances, stretching alone is not sufficient to correct the dimensional tolerances of a straight tube to meeting automotive tolerance requirements.
This disclosure is directed to solving the above problems and other problems as summarized below.